The present invention relates to an apparatus for applying and curing ink on optical fibers. More particularly, the present invention relates to an improved nitrogen injection assembly for use with a coating die assembly that applies ink to an optical fiber and a curing chamber that cures the ink with ultraviolet (UV) radiation.
Optical fibers are often colored to improve their identification and indexing. For example, a telecommunications worker can more easily distinguish one optical fiber from another when making splices between optical fiber cables if the fibers have distinctive colors.
The process for coloring optical fibers entails two basic steps. First, during the manufacture of the optical fiber, the drawn fiber is coated with ink by passing it through a coloring die assembly. Second, the ink is cured by passing the coated fiber through a chamber of UV radiation. Generally, this process is used for both individual optical fibers and for optical fibers that are formed into ribbons.
Inks used for coloring optical fibers typically do not adhere properly to optical fibers in the presence of oxygen. Consequently, the coloring inks are typically cured on optical fibers in a nitrogen environment. To ensure the absence of oxygen from the curing process, a nitrogen injection assembly is positioned between the coating die assembly and the UV curing chamber. The nitrogen injection assembly provides a passageway for the optical fiber between the coating die assembly and the curing chamber. An upper portion of the nitrogen injection assembly adds nitrogen to the passageway.
A lower portion of the nitrogen injection assembly is typically defined by a telescoping tube. In a setup mode, the telescoping tube is collapsed to provide access to the optical fiber. After-threading the optical fiber through the coloring die, an operator can access the fiber and attach it to a leader. The leader helps pull the fibers through the optical fiber coloring and curing apparatus. In an operating mode, the telescoping tube is extended to create a cylindrical passageway for the optical fiber between the nitrogen injection assembly and the curing chamber. Various seals ensure an airtight connection, keeping in nitrogen and keeping out oxygen from the ambient environment.
FIG. 1 illustrates a conventional nitrogen injection assembly for use in coating and curing ink on an optical fiber. This nitrogen injection assembly 100 generally comprises a nitrogen injection ring 108 mounted to the underside of a coloring die mounting plate 104. Coloring die mounting plate 104, which is part of a coloring die assembly, and nitrogen injection ring 108 both have central bores through which the drawn fiber passes. Nitrogen gas is injected into the bore in nitrogen injection ring 108 through a side port 152.
Below nitrogen injection ring 108 is a telescope tube. The tube includes a telescope tube holder ring 112 proximate to nitrogen injection ring 108. Holder ring 112 has a central bore that matches the bores of coloring die mounting plate 104 and nitrogen injection ring 108. The optical fiber passes through the central bore in holder ring 112. Both holder ring 112 and nitrogen injection ring 108 are attached to coloring die mounting plate 104 via screws or bolts in first threaded mounting hole 132, second screw hole 136, and third screw hole 140.
The telescope tube itself is made of a stationary telescope tube 116 and a sliding telescope tube 120. The sliding telescope tube 120, which has a larger diameter, fits around and slides over stationary telescope tube 116. By sliding telescope tube 120 up in a retracted position over stationary telescope tube 116, an operator can gain access to the fiber to attach it to a leader. When sliding telescope tube 120 is extended, it contacts a base 124 to create a sealed environment for the nitrogen to travel into the curing chamber (not shown). Base 124 has a central bore matching that of the telescope tube assembly and is mounted to the curing chamber (not shown).
During operation, when sliding telescope tube 120 is extended, nitrogen injection assembly 100 adds nitrogen via port 152 to the central bores defined by nitrogen injection ring 108, stationary tube 116, sliding tube 120, and base 124. The nitrogen in general flows downwardly with the moving optical fiber through these bores and into the curing chamber. Because the nitrogen gas is injected near the top of nitrogen injection assembly 100, potential leak points must be sealed to ensure the absence of oxygen from the UV curing chamber. If leaks exist, oxygen from the ambient atmosphere may be drawn into the nitrogen injection assembly 100, possibly via a Ventura effect, as the nitrogen travels down the bore and into the UV curing chamber.
O-rings 156, 160, 164, 168, 172 and 176 seal the components of nitrogen injection assembly 100 at various potential leak points. A first O-ring 156 is positioned between coloring die mounting plate 104 and nitrogen injection ring 108. A second O-ring 172 is positioned between holder ring 112 and nitrogen injection ring 108. Third and fourth O-rings 160 and 164 are positioned between the outer diameter of stationary telescope tube 116 and the inner diameter of sliding telescope tube 120. A fifth O-ring 168 is located between base 124 and the inner diameter of sliding telescope tube 120. A sixth O-ring 176 is positioned between base 124 and a UV oven 128.
Applicants have found that this conventional nitrogen injection assembly has a few disadvantages. The number of potential leak points and the number of O-rings makes the assembly particularly susceptible to ambient air leaks that can disrupt the curing process. These O-rings are not quickly and easily repaired. Additionally, the assembly hampers efficient setup for the coating process. In particular, the space provided by sliding telescope tube 120 is relatively confined for an operator to attach a leader to the drawn fiber. Consequently, the risk of breaking a fiber is often higher than desired.
A second prior art configuration is illustrated by Japanese Patent No. 4-342445. The apparatus disclosed in JP 4-342445 provides for the coloring of an optical fiber in an oxygen-free environment. A “connection means,” located between a coating apparatus and a curing oven, forms a sealed cylindrical conduit for passing an optical fiber. In this prior art configuration, the optical fiber is coated with uncured dye, passed through the “connection means,” and fed into the curing chamber—all in an environment containing pure nitrogen. In this manner, the connection means of JP 4-342445 forms an air-tight seal between the coating apparatus and the curing oven allowing the entire coating and curing process to be performed in an oxygen-free environment.
The apparatus disclosed in JP 4-342445 suffers from many of the same disadvantages as the prior art apparatus disclosed in FIG. 1. In addition, this conventional nitrogen injection assembly unnecessarily prevents the exposure of uncured dye to oxygen.